[Raph] had a pair of foam mattresses from ... 50 V 20 A variable DC power supply. [Raph] determined the current experimentally: the wire failed at 20 A, and cutting speed was too low at 12 A.

Cutting foam is pretty tricky without a hot wire cutter ... [Darcy] is using an old 9V power wart that he had lying around, but you can probably use any DC power supply. He designed the frame ...